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First, What exactly does the polishing part of "porting and polishing" the intake manifold do? I'm pretty sure that i know porting it means opening the holes bigger letting more air and such in. Also, I am wondering if forged pistons give a gain, or if they are the same compression. And how much of a gain would high compression pistons give me? I only have a 4cyl with a home depot intake. I would like more power, and have also thought of doing the jspec cams. Last thing... how hard is it to replace the pistons. Would i have to take the whole engine apart to get the crankshaft out to put the pistons on? If i were to get a shop to do it, what do you guys think would be a good estimate of the cost. Thanks a lot


XO looks like a kodama for those of you who have watched princess mononoke
 

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Burningcrap said:
First, What exactly does the polishing part of "porting and polishing" the intake manifold do? I'm pretty sure that i know porting it means opening the holes bigger letting more air and such in.
Polishing, as the name implies, means smoothing the port and runner surfaces. Imagine running your hand along a smooth table top and them a length of 120-grit sandpaper.

Be aware that not everyone endorses polishing of ports because while the concept of friction reduction is noble, the model is oversimplified and ignores fluid mechanics like boundary layers. For an example, study up on why golf balls have dimples instead of being perfectly smooth.

Also, I am wondering if forged pistons give a gain, or if they are the same compression.
No, not if they yield the same compression ratio. They will let you run more NOS and/or turbo boost though. They may also be noisier, especially when cold since forged pistons require larger clearances (they expand more when hot).

And how much of a gain would high compression pistons give me? I only have a 4cyl with a home depot intake.
Bumps in compression usually result in about 4%/point. So going from 9:1 to 10:1 would give a 4% bump in power.

Last thing... how hard is it to replace the pistons. Would i have to take the whole engine apart to get the crankshaft out to put the pistons on?
Technically, you can remove the pistons & rods from the engine in situ but I'd be very wary of this. For instance, when installing new rings (with the new pistons) you'll need to re-hone the cylinder walls to break the glaze or the new rings won't seat. Honing produces metal bits that will fall down onto the crank etc. Tough to thoroughly clean. Also, once apart, if you measure the cylinder walls and find them worn or out of spec, you'll need to bore anyway (which must be done out of the car.)
 
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